Tour bus crash investigation underway in Alberta

Investigators in Alberta continue to probe a deadly tour bus crash at the Columbia Icefield in the Rocky Mountains, between Banff and Jasper.

Just what caused the big-wheeled vehicle to overturn remains a mystery.

Dave McKenna, the president of the company that operates the sightseeing tour, says they've begun their own investigation into the cause as well.

Three people were killed in the Saturday accident, while two dozen more were injured, 14 of them critically.

There has been speculation a rock slide may have played a role in the accident, but investigators have not confirmed that.